A device of such a type may come into operation, for example, within the scope of a microkeratome, i.e. in the case of a microsurgical plane such as is used, for example, for the placement of a flap incision on a human eye. Such a flap incision is necessary within the scope of a form of operation customarily known in specialist circles as LASIK (laser in-situ keratomileusis). By means of the flap incision, in this case on the surface of the cornea a small disc (flap) is cut out which on a part of its periphery is still connected to the remaining corneal tissue and can therefore be folded aside and subsequently folded back again without difficulty. Depending on whether the flap incision extends within the stroma or within the epithelium on Bowman's membrane, in specialist circles one customarily speaks of classical LASIK or Epi-LASIK, respectively.
In the case of a microkeratome, the suction ring is needed not only for the purpose of fixing the eye but customarily also for the purpose of coupling and guiding a cutting unit equipped with a cutting blade, which, as a rule, is held in the hand by the operating surgeon and is therefore frequently also designated as a handpiece of the microkeratome. Also customarily part of the handpiece is a motorised drive unit which serves for generating the cutting motion of the cutting blade. In the case of a microkeratome marketed by WaveLight under the trade name RONDO, the cutting blade has, like a razor, a rectilinear cutting edge and is moved linearly, subject to high-frequency lateral oscillation, in the direction perpendicular to the cutting edge. The cutting blade is, for example, held in a cutting head which is separably and consequently interchangeably coupled with a drive module of the handpiece.
The suction-ring instrumentarium may include, in addition to the actual suction ring, further components which, for example, serve for transmitting the vacuum from the interface port to the suction ring. For example, these components may include a hose line with a suitable connector for connecting to the interface port. At the end remote from the interface this hose line may have been separably connected to a connecting piece of a suction-ring unit forming the suction ring and, for example, produced in one piece. It should be pointed out that the suction-ring unit may perfectly well exhibit several hose-line ports which permit the attachment of several hose lines, particularly if the suction-ring unit exhibits several evacuation spaces (suction chambers) that are capable of being evacuated separately. For the purpose of fixing the suction ring to the eye, said suction ring customarily exhibits an annular chamber delimited exclusively between the suction ring and the surface of the eye.
A device according to the invention may, alternatively or additionally, come into operation within the scope of a cutting machining of the human eye using laser technology. Relevant laser systems often provide for the interposition of an adapter between the eye to be machined and an objective which focuses the laser radiation onto the eye. The adapter brings about a positioning of the eye in relation to the laser system, facilitating the accurately targeted generation of the incision. In this connection it is known to construct the adapter with a contact element that is transparent to the laser radiation and that is brought into planar contact with the eye. In the case of a plane contact surface of the contact element, a levelling of the cornea takes place; one therefore speaks of an applanation element.
By reciprocal coupling of the suction ring, which in turn is firmly aspirated on the eye, and of the adapter, for instance by aspirating the adapter onto the suction ring, it is possible to position the eye precisely and securely in relation to the laser system.
Regardless of the form of the operation in which the suction-ring instrumentarium is being employed, a sufficiently intense vacuum is necessary, in order that the suction ring remains firmly aspirated on the eye reliably during the operation. As a rule, the vacuum-pump arrangement is dimensioned so as to be sufficiently powerful in order to be able to build up the requisite vacuum under normal conditions. An overdimensioning of the vacuum-pump arrangement is of course not desirable as a rule, for reasons of cost and construction space.
The achievable quality of the vacuum depends not only on the maximal pumping power of the vacuum-pump arrangement but also on the altitude of the location of use and on the current weather situation. For given pumping power, the achievable vacuum pressure depends on the current atmospheric pressure at the location of use, in which connection this atmospheric pressure may fluctuate more or less intensely, depending on the altitude of the location of use and depending on the state of the weather (high pressure, low pressure). This may have the consequence that, under certain circumstances, in the case of a location of use situated at a great height only a considerably smaller operating range of the vacuum than under lowland conditions is available. Even if the user presets a certain nominal value of the relative underpressure (‘relative underpressure’ means the level of the underpressure in relation to the environment) at an operating console, the relative underpressure actually achieved may be substantially lower (e.g. −500 mmHg instead of a value desired by the user of, for example, −600 mmHg) and therefore may under certain circumstances give rise to surgical dangers.